GCN Circular #13405
T. Sakamoto (GSFC/UMBC), S. D. Barthelmy (GSFC), Gehrels (GSFC),
E. Sonbaas (GSFC) (for the Swift-BAT team);
O. Littlejohns (U. Leicester) (for the Swift-XRT team);
S. R. Oates (MSSL-UCL) (of the Swift-UVOT team):
Using the data set from T-60 to T+243 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 120630A (trigger #525451).
There was no initial set of GCN Notices nor a rapid-response circular
because of the power outage at GSFC when this burst occurred.
Swift slewed immediately to the burst location.
The BAT ground-calculated position is RA, Dec = 352.300, 42.495 deg, which is
RA(J2000) = 23h 29m 12.0s
Dec(J2000) = +42d 29' 41.5"
with an uncertainty of 2.7 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 65%.
The mask-weighted light curve shows a single spike starting at ~T-0.05 sec
and ending at ~T+0.65 sec. T90 (15-350 keV) is 0.6 +- 0.2 sec
(estimated error including systematics).
The time-averaged spectrum from T-0.1 to T+0.6 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.04 +- 0.43. The fluence in the 15-150 keV band is 6.1 +- 1.4 x 10^-8 erg/cm2.
The 1-sec peak photon flux measured from T-0.25 sec in the 15-150 keV band
is 0.7 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence level.
Given the short duration and the hard spectrum of this burst,
it is very likely a short GRB.
The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/525451/BA/ .
We have analysed 1.4 ks of XRT data for GRB 120630A from 97 s to 1.5 ks
after the BAT trigger. The data are entirely in Photon Counting (PC) mode.
The refined XRT position is RA, Dec = 352.29481, 42.55483 which is equivalent to:
RA (J2000): 23 29 10.75
Dec(J2000): +42 33 17.4
with an uncertainty of 3.9 arcsec (radius, 90% confidence).
The light curve can be modelled with a power-law decay with a decay index
of alpha=1.7 (+/-0.5).
A spectrum formed from the PC mode data can be fitted with an absorbed power-law
with a photon spectral index of 1.7 (+/-0.4). The best-fitting absorption column
is consistent with the Galactic value of 8.8 x 10^20 cm^-2 (Kalberla et al. 2005).
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced
from this spectrum is 4.2 x 10^-11 (4.9 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 0 (+2.2, -0) x 10^21 cm^-2
Galactic foreground: 8.8 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index: 1.7 (+/-0.4)
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00525451 .
The Swift/UVOT began settled observations of the field of GRB 120630A
150 s after the BAT trigger (trigger #525451). No optical afterglow
consistent with the refined XRT position nor with the candidate optical
afterglow (Xu et al., GCN Circ. 13403) is detected in the initial UVOT
exposures. Preliminary 3-sigma upper limits using the UVOT photometric
system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first
finding chart (FC) exposure and subsequent exposures are:
Filter T_start(s) T_stop(s) Exp(s) Mag
v 457 1409 117 >19.0
b 406 1508 156 >20.0
u_FC 150 400 246 >20.2
u 150 1032 393 >20.3
uvw1 506 1458 117 >19.3
uvm2 481 1434 97 >19.0
uvw2 432 1530 131 >19.5
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.106 in the direction of the burst
(Schlegel et al. 1998).
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